Human norovirus GII.4 Hong Kong variant shares common ancestry with GII.4 Osaka and emerged in Thailand in 2016.

Human norovirus is a leading cause of non-bacterial acute gastroenteritis, which affects all age groups and are found globally. Infections are highly contagious and often occur as outbreaks. Periodic emergence of new strains are not uncommon and novel variants are named after the place of first reported nucleotide sequence. Here, we identified human norovirus GII.4 Hong Kong variant in stool samples from Thai patients presented with acute gastroenteritis. Comparison of amino acid residues deduced from the viral nucleotide sequence with those of historical and contemporary norovirus GII.4 strains revealed notable differences, which mapped to the defined antigenic sites of the viral major capsid protein. Time-scaled phylogenetic analysis suggests that GII.4 Hong Kong shared common ancestry with GII.4 Osaka first reported in 2007, and more importantly, did not evolve from the now-prevalent GII.4 Sydney lineage. As circulation of norovirus minor variants can lead to eventual widespread transmission in susceptible population, this study underscores the potential emergence of the GII.4 Hong Kong variant, which warrants vigilant molecular epidemiological surveillance.